210 



MONTOOMKHY A STUDY OF THE CHROMOSOMES 



halving of the number jnsl. before the maturation mitoses is not a real halving of the 

 normal Dumber, but only a grouping into pairs. And the mantle fibres, those which 

 connect the centrosomes with the chromosomes, seem in fact to have their number deter- 

 mined to some extent by the number of the chromosomes, and not to determine that number, 

 for the definite number of chromosomes appear in mitosis before the mantle fibres arise. 

 The number of the connective fibres, those which connect corresponding daughter 

 chromosomes in the anaphase, is certainly determined by I he number of the chromosomes, 

 for these fibres are stretched-out portions of the linin matrices of the chromosomes. 

 Thus the centrosomes and the achromatic spindle structures may play a part in the dis- 

 tribution of the chromosomes, but apparently have no part in the determination of their 

 number. 



As for the true nucleoli, their number, volume and position seem to be in no way 

 regulative of the chromosomal number. The nucleolar number in one species is gener- 

 ally variable, and correlatively also the volume and position, while the chromosomal 

 number is constant ; in the paternal germ cells the number of nucleoli is frequently 

 different (and generally smaller) than that in the maternal cells of a species, but in both 

 kind of cells the number of chromosomes is the same. 



The mass of the nucleus or of the cell body, or the relative mass of the two, might 

 seem a priori to stand in connection with the chromosomal number, yet an examination 

 of the facts shows this is probably not the case. For instance, in one species the huge 



ovocytes and the much smaller spermatocytes haves the same number of chromos es, and 



a small ovogonium bas the same number of chromosomes as a large ovocyte. And in the 

 case of the ovocyte the volume of the nucleus is relatively small, in the spermatocyte rela- 

 tively large in proportion to the maws of the cell body, yet the number of the chromo- 

 somes is the same. The mass of the chromatin substance maybe mores or less proportion- 

 ate to the volume of the nucleus, but the number of the chromosomes appears not to be ; the 

 large number of chromosomes in Arlemia (as determined by I'rauer) is not correlated 

 with a, large nucleus; and as the figures of the present paper show, cells of approximately 

 tins same size from different species may show very different chromosomal numbers. The 

 form of the cell is regulated to great extent- by external influences, and variations in tins 

 Conn products no modification of the chromosomal number. 



The volume of the chromosomes in mitosis is dependent upon their number, since 

 the volume of the chromatin stands in mores or less direct ratio to the volume of tins 

 nucleus. The form of the chromosomes is more or less dependent upon their number, 

 inasmuch as long ribbon-shaped chromosomes occur only where there are a small number, 

 and rou nded ones where there are a larger number present, Yet in all the Hemiptera, 

 with their considerable differences' in chromosomal number, the form of the chromosomes 



